Venezuelan Bolivarian National police move away from the flames after an explosion at Altamira square during clashes against anti-government demonstrators in Caracas, Venezuela, Sunday, July 30, 2017. AP

Venezuela's chief prosecutor's office is reporting three deaths on the day of a controversial vote for a constituent assembly that opposition leaders fear will trigger the end of democracy in Venezuela.

The office tweeted that 28-year-old Angelo Mendez and 39-year-old Eduardo Olave were killed at a protest Sunday in Merida. Thirty-year-old Ricardo Campos was killed in a separate incident in Sucre.

Few details were provided on the deaths.

Leaders with the opposition Democratic Action party on Twitter identified Campos as the group's youth secretary in Sucre, a state in northern Venezuela east of the nation's capital.

The deaths bring to at least 116 those killed in nearly four months of political upheaval.

The government says the constituent assembly is the only way to bring peace back to the country after months of violent protests.

The election has been heavily criticised by other Latin American countries as well as the European Union and the United States, which last week imposed new sanctions on members of Mr Maduro's government.

Venezuela, a major oil producer, is gripped by a political crisis, with soaring inflation and daily food shortages.